Combustion engines that run on fossil fuels generate exhaust gases. The exhaust gases typically include oxygen as well as various undesirable pollutants. Non-limiting examples of undesirable pollutants include nitrogen oxide gases (NOx), unburned hydrocarbon gases (HC), and carbon monoxide gas (CO). Various industries, including the automotive industry, use exhaust gas sensors to both qualitatively and quantitatively sense and analyze the composition of the exhaust gases for engine control, performance improvement, emission control and other purposes, such as to sense when an exhaust gas content switches from a rich to lean or lean to rich air/fuel ratio. For example, HC emissions can be reduced using sensors that can sense the composition of oxygen gas (O2) in the exhaust gases for alteration and optimization of the air to fuel ratio for combustion.
A conventional high temperature gas sensor typically includes an ionically conductive solid electrolyte material, a porous electrode on the sensor's exterior exposed to the exhaust gases with a porous protective overcoat, a porous electrode on the sensor's interior surface exposed to a known gas partial pressure, an embedded resistance heater and electrical contact pads on the outer surface of the sensor to provide power and signal communication to and from the sensor. An example of a sensor used in automotive applications uses a yttria-stabilized, zirconia-based electrochemical galvanic cell with porous platinum electrodes to detect the relative amounts of oxygen present in an automobile engine's exhaust. When opposite surfaces of this galvanic cell are exposed to different oxygen partial pressures, an electromotive force (emf) is developed between the electrodes on the opposite surfaces of the electrolyte wall, according to the Nernst equation.
Exhaust sensors that include various flat-plate ceramic sensing element configurations formed of various layers of ceramic and electrolyte materials laminated and sintered together with electrical circuit and sensor traces placed between the layers, and embedded resistance heaters and electrical contact pads on the outer surface of the sensor to provide power and signal communication to and from the sensors have become increasingly popular. These flat-plate sensors generally have a sensing portion or end, that is exposed to the exhaust gases, and a reference portion or end, that is shielded from the exhaust gases providing an ambient reference. Gas sensors that employ these elements generally use high temperature electrical connectors for the electrical connection to contact pads on the reference end of the sensor to provide the necessary power and signal communication between a vehicle controller and the gas sensor. These electrical connectors are exposed to the extreme operating temperatures of internal combustion engine exhaust systems, which may include temperatures at the connector of greater than 200° C. and up to about 350° C. Thus, these connectors generally have connector bodies made from high temperature materials, such as ceramics.
These connectors also include conductive terminals which are generally disposed within the ceramic body portions and provide both contact portions to make the necessary electrical contact with the contact pads a termination portion for attachment to wires for communication with the controller. The connectors, including the ceramic body portions and terminals, must be designed so as to receive the ceramic gas sensor with a relatively low insertion force, but to have a relatively higher contact force in operation to ensure the reliability of the communications between the controller and the sensor. Various edge card connectors have been proposed for use in high temperature gas sensors. These connectors simply plug on the end of the gas sensor; however, they frequently require relatively high (e.g., greater than 2 lbf insertion forces). In these connectors, the positions of the connector bodies and terminals are fixed, and, where high temperature ceramic connector bodies are used, relatively non-resilient as compared to lower temperature connectors with polymeric connector bodies, due to the mechanical properties of the ceramics. Thus, upon insertion of the sensor, its contact pads have the full contact force of the connector terminals applied as the respective contacts slide under the terminals into the installed position. Damage to the contact pads frequently occurs; with the result that edge card connectors are generally undesirable for many gas sensor applications. One such connector has proposed a clamshell configuration where opposing halves of a ceramic connector body open in a clamshell configuration to receive the gas sensor, whereupon the halves of the sensor are closed to establish electrical contact between conductive terminals disposed on the respective connector halves and the contact pads on the gas sensor. Upon closing the connector halves, a solid metal connector retaining ring is disposed around them to retain the connector body portions and establish the operating contact force between the terminals and the contact pads.
While various high temperature electrical connector configurations have been proposed, there remains a need for improved high temperature connectors, including those having configurations which provide improved sensor insertion characteristics while maintaining sufficient contact forces after insertion, and which have designs which facilitate assembly and installation of the connector.